Synthesis and preclinical evaluation of [11C]MA-PB-1 for in vivo imaging of brain monoacylglycerol lipase (MAGL).

MAGL is a potential therapeutic target for oncological and psychiatric diseases. Our objective was to develop a PET tracer for in vivo quantification of MAGL. We report [11C]MA-PB-1 as an irreversible MAGL inhibitor PET tracer. The in vitro inhibitory activity, ex vivo distribution, brain kinetics and specificity of [11C]MA-PB-1 binding were studied. Ex vivo biodistribution and microPET showed good brain uptake which could be blocked by pretreatment with both MA-PB-1 and a structurally non-related MAGL inhibitor MJN110. These initial results suggest that [11C]MA-PB-1 is a suitable tracer for in vivo imaging of MAGL.

Synthesis, Biodistribution and In vitro Evaluation of Brain Permeable High Affinity Type 2 Cannabinoid Receptor Agonists [11C]MA2 and [18F]MA3.

The type 2 cannabinoid receptor (CB2) is a member of the endocannabinoid system and is known for its important role in (neuro)inflammation. A PET-imaging agent that allows in vivo visualization of CB2 expression may thus allow quantification of neuroinflammation. In this paper, we report the synthesis, radiosynthesis, biodistribution and in vitro evaluation of a carbon-11 ([11C]MA2) and a fluorine-18 ([18F]MA3) labeled analog of a highly potent N-arylamide oxadiazole CB2 agonist (EC50 = 0.015 nM). MA2 and MA3 behaved as potent CB2 agonist (EC50: 3 nM and 0.1 nM, respectively) and their in vitro binding affinity for hCB2 was found to be 87 nM and 0.8 nM, respectively. Also MA3 (substituted with a fluoro ethyl group) was found to have higher binding affinity and EC50 values when compared to the originally reported trifluoromethyl analog 12. [11C]MA2 and [18F]MA3 were successfully synthesized with good radiochemical yield, high radiochemical purity and high specific activity. In mice, both tracers were efficiently cleared from blood and all major organs by the hepatobiliary pathway and importantly these compounds showed high brain uptake. In conclusion, [11C]MA2 and [18F]MA3 are shown to be high potent CB2 agonists with good brain uptake, these favorable characteristics makes them potential PET probes for in vivo imaging of brain CB2 receptors. However, in view of its higher affinity and selectivity, further detailed evaluation of MA3 as a PET tracer for CB2 is warranted.

New transient receptor potential vanilloid subfamily member 1 positron emission tomography radioligands: synthesis, radiolabeling, and preclinical evaluation.

The transient receptor potential vanilloid subfamily member 1 (TRPV1) cation channel is known to be involved in pain nociception and neurogenic inflammation, and accumulating evidence suggests that it plays an important role in several central nervous system (CNS)-related disorders. TRPV1-specific positron emission tomography (PET) radioligands can serve as powerful tools in TRPV1-related (pre)clinical research and drug design. We have synthesized several potent TRPV1 antagonists and accompanying precursors for radiolabeling with carbon-11 or fluorine-18. The cinnamic acid derivative [(11)C]DVV24 and the aminoquinazoline [(18)F]DVV54 were successfully synthesized, and their biological behavior was studied. In addition, the in vivo behavior of a (123)I-labeled analogue of iodo-resiniferatoxin (I-RTX), a well-known TRPV1 antagonist, was evaluated. The binding affinities of DVV24 and DVV54 for human TRPV1 were 163 ± 28 and 171 ± 48 nM, respectively. [(11)C]DVV24, but not [(18)F]DVV54 or (123)I-RTX, showed retention in the trigeminal nerve, known to abundantly express TRPV1. Nevertheless, it appears that ligands with higher binding affinities will be required to allow in vivo imaging of TRPV1 via PET.

Synthesis and biological evaluation of [¹¹C]SB366791: a new PET-radioligand for in vivo imaging of the TRPV1 receptor.

INTRODUCTION: The transient receptor potential vanilloid subfamily member 1 (TRPV1) receptor, a non-selective cation channel, is known for its key role in pain nociception and neurogenic inflammation. TRPV1 expression has been demonstrated in diverse tissues and an essential role for TRPV1 in various disorders has been suggested. A TRPV1-specific PET-radioligand can serve as a useful tool for further in vivo research in animals and directly in humans. In this study, we report the synthesis and biological evaluation of a carbon-11 labelled analogue of N-(3-methoxyphenyl)-4-chlorocinnamide (SB366791) which was reported as a specific high-affinity antagonist for TRPV1. METHODS: The new tracer was evaluated with respect to log D and biodistribution in control, pretreated and TRPV1⁻/⁻ mice. The percentage of radiometabolites of [¹¹C]SB366791 was determined in mouse plasma and brain. RESULTS: [¹¹C] SB366791 was obtained in good yield (69%±11%; isolated amounts 3034-5032MBq) and high specific activity (390±215 GBq/µmol). The tracer was efficiently cleared from blood and all major organs via hepatobiliary and renal pathways. Initial brain uptake was high (1.6% ID) and wash-out from brain was rapid. The retention of [¹¹C] SB366791 in the trigeminal nerve of control mice was prominent. The in vitro binding affinity of SB366791 was determined to be 280±56 nM and 780±140 nM for human and rat TRPV1, respectively. CONCLUSIONS: [¹¹C] SB366791 has favourable biodistribution characteristics in mice. However the obtained low binding affinity for TRPV1 may not be sufficient to use the current compound as PET tracer.

Small-animal PET imaging of the type 1 and type 2 cannabinoid receptors in a photothrombotic stroke model.

PURPOSE: Recent ex vivo and pharmacological evidence suggests involvement of the endocannabinoid system in the pathophysiology of stroke, but conflicting roles for type 1 and 2 cannabinoid receptors (CB(1) and CB(2)) have been suggested. The purpose of this study was to evaluate CB(1) and CB(2) receptor binding over time in vivo in a rat photothrombotic stroke model using PET. METHODS: CB(1) and CB(2) microPET imaging was performed at regular time-points up to 2 weeks after stroke using [(18)F]MK-9470 and [(11)C]NE40. Stroke size was measured using MRI at 9.4 T. Ex vivo validation was performed via immunostaining for CB(1) and CB(2). Immunofluorescent double stainings were also performed with markers for astrocytes (GFAP) and macrophages/microglia (CD68). RESULTS: [(18)F]MK-9470 PET showed a strong increase in CB(1) binding 24 h and 72 h after stroke in the cortex surrounding the lesion, extending to the insular cortex 24 h after surgery. These alterations were consistently confirmed by CB(1) immunohistochemical staining. [(11)C]NE40 did not show any significant differences between stroke and sham-operated animals, although staining for CB(2) revealed minor immunoreactivity at 1 and 2 weeks after stroke in this model. Both CB (1) (+) and CB (2) (+) cells showed minor immunoreactivity for CD68. CONCLUSION: Time-dependent and regionally strongly increased CB(1), but not CB(2), binding are early consequences of photothrombotic stroke. Pharmacological interventions should primarily aim at CB(1) signalling as the role of CB(2) seems minor in the acute and subacute phases of stroke.

Development of a validated liquid chromatographic method for the determination of related substances and assay of tenofovir disoproxil fumarate.

The present study describes the development and validation of a selective liquid chromatographic (LC) method for the analysis of tenofovir disoproxil fumarate (TDF) and its related substances. The gradient method uses a base deactivated C18 column (Hypersil BDS column; 25 cmx4.6 mm I.D.) maintained at a temperature of 30 degrees C. The mobile phases consist of acetonitrile, tetrabutylammonium/phosphate buffer pH 6.0 and water: (A; 2:20:78 v/v/v) and (B; 65:20:15 v/v/v). The flow rate is 1.0 mL/min and UV detection is performed at 260 nm. Good separation of TDF and 21 impurities was achieved. A system suitability test (SST) to check the quality of separation is also specified. The developed method was further validated with respect to robustness, precision, sensitivity and linearity. The method is proved to be robust, precise, sensitive and linear between 0.1 microg/mL and 0.15 mg/mL. The limit of detection and limit of quantification are 0.03 and 0.1 microg/mL, respectively. The method was successfully applied to the quantification of related substances and assay of commercial TDF samples (bulk substances and tablets).